The present invention relates generally to defect detection apparatus and method for detecting defects in food products such as French-fry potato strips or other articles, including wood products, by light reflection and, in particular, to such defect detection apparatus and method employing pulsed light-emitting semiconductor devices for irradiating the products under investigation with light of different wavelengths and optical sensors with photoelectric detectors for detecting the light reflected from such products to determine whether they contain any defects.
It has been previously proposed in U.S. Pat. No. 4,576,071 of A. G. Rayment issued Mar. 18, 1986, for "Food Product Defect Sensor and Trimmer Apparatus" to provide a food product sensor and trimmer apparatus for detecting and removing defects from French-fry potato strips. The defect detector employs light sources in the form of incandescent light bulbs or halogen gas-filled lamps which generate "white" light of all visible frequencies and infrared light frequencies. Beam splitters in the form of hot mirrors and filters are used to separate such white light into beams of two different wavelengths including visible light and near-infrared (NIR) light. This prior defect detection apparatus had the disadvantage that such white light sources were ON substantially continuously and were of high power to provide sufficient light intensity which resulted in short useful lifetime and excessive heat buildup. It has been found that by using pulsed light-emitting semiconductor devices such as light-emitting diodes (LEDs), the short lifetime and excessive heat problems are solved, and sufficiently high intensity light is produced with a small fraction of the power dissipation previously required. As a result, pulsed LED light sources have a useful life at least ten times as long as the incandescent bulbs or the halogen gas light bulbs previously employed. In addition, the viewing apparatus is greatly simplified by elimination of the need for beam-splitting mirrors and filters since the desired color or wavelength of the light used to irradiate the product being tested for defects can be obtained directly from the LED. Thus, the correct wavelength light is obtained merely by selecting a light-emitting semiconductor device of the type whose light output is of the wavelength desired. This also enables the use of more than the two colors or wavelengths of light that are employed in the Rayment patent discussed above. Thus, by employing at least three different, separated wavelengths of light, the present defect detection apparatus is better able to detect defects and to distinguish between different types of defects.
Also of interest is U.S. Pat. No. 4,656,904 of A. G. Rayment issued Apr. 14, 1987, for "Food Product Cutter Apparatus" which discloses an improved cutter that may be employed in the defect sensor and trimmer apparatus of the above-discussed Rayment patent.
As disclosed in U.S. Pat. No. 4,520,702 of W. L. Davis, et al., issued June 4, 1985, for "Inspection and Cutting Apparatus," it has been proposed to provide an article inspection and cutting apparatus in which elongated articles such as French-fry potato strips are transmitted past scanning cameras to detect defects therein by sensing visible light reflected from such articles. The visible light emitted by a bank of incandescent lamps or fluorescent lamps apparently is white light containing all the wavelengths of visible light. Such apparatus does not provide light beams of different wavelengths in the manner of the above-described Rayment patent. In order to increase the intensity of illumination, the lamp bank is pulsed at a frequency synchronized to the scanning rate of the camera. The defect detection apparatus of the present invention is considerably faster and more accurate than that of Davis in that it does not employ a scanning camera. The scanning camera of Davis includes an electronically scanned linear diode array. However, the present invention employs a single diode photocell as a light sensor and employs light-emitting semiconductor devices, such as LEDs, as direct sources of different wavelength light to detect defects and to distinguish between different defects.
Also, unlike the above-discussed patents, in the present defect detection apparatus the LEDs are pulsed by a capacitor discharge circuit which provides a pulse of substantially constant current to cause light of substantially uniform intensity to be emitted therefrom.
It has been disclosed in U.S. Pat. No. 3,887,836 of Leete, issued June 3, 1975, for "Optical Driver Circuit," and U.S. Pat. No. 3,898,588 of Skagerlund, issued Aug. 5, 1975, for "Diode Laser Pumping" to provide light-emitting semiconductor devices such as LEDs which are pulsed ON by discharging a storage capacitor through such diodes. However, such LEDs are not employed in defect detection apparatus in the manner of the present invention.